It is well understood that attempts to maintain viable hydrocarbon supplies have necessitated the exploitation of more marginal hydrocarbon production zones. It is also well known that exploiting marginal hydrocarbon production zones requires the use of sophisticated well drilling techniques, such as horizontal drilling and multi-stage well completions. It is further known that marginal production zones generally require stimulation in order to be viable producers of hydrocarbons. As understood by those skilled in the art, the stimulation of hydrocarbon production zones generally requires pumping high-pressure fluids into the zones. In order to accomplish this, pressure-sensitive wellhead equipment must be protected during the stimulation process.
Many wellhead isolation tools have been developed to protect sensitive wellhead equipment while high pressure stimulation fluids are pumped into subterranean formations. A high-pressure mandrel of the wellhead isolation tool, commonly referred to as a “frac mandrel” provides the pressure isolation through the wellhead. Some wellhead isolation tools also provide full-bore access to a casing of the well in order to permit downhole operations such as logging, perforating and plugging to be performed through the tools. However, prior art wellhead isolation tools have known disadvantages. For example, they are expensive to use due to labor costs associated with delivering and operating them; they cannot be removed from a live well; or they are known to “get stuck” in the wellhead making them difficult or impossible to remove without killing or plugging a casing of the well.
There therefore exists a need for a retrievable frac mandrel with a well control stack that can be left on a wellhead throughout a well completion, re-completion or workover, and that can be removed from the wellhead without killing the well or plugging the casing.